Syringe

ABSTRACT

A lightweight syringe is provided having a plastic foam plunger. The plunger is of unitary construction made of a plastic foam material and dimensioned so as to fit in the syringe body whereby the plastic foam material forms a resilient compression seal. The syringe can be disposed of after single use, or can be sterilized and reused, at the option of the user.

United States Patent Rubricius 1 Apr. 18, 1972 [54] SYRINGE 2,641,093 6/1953 Kolodny et a1 ..128/218 P X 2,649,090 8/1953 Parsons et a1 ..128/272 [72] Inventor. Jeanette Lois Rllbl'lClllS, New York, NY. 3,026,872 3/1962 Prater Jr i 128 /218 P [73] Assignee: Harry H. Leveen, Brooklyn, NY. 3,045,674 7/1962 Goldberg... ..128/218 P [22] Filed: June 17, 1969 3,176,595 4/1965 Schwartz ..128/218 P 11X [21 1 AW 834,020 FOREIGN PATENTS OR APPLICATIONS 1,158,414 1/1958 France ..128/218 P 52 us. Cl ..128/218 P 212,652 3/1924 Great Britain -128/218 P [51] Int. Cl. ..A6lm 05/22 [58] FieldofSearch ..128/218,2l8 P, 221,272;

Primary Examiner.loseph S. Reich AttorneyMarn & .langarathis [5 7] ABSTRACT A lightweight syringe is provided having a plastic foam plunger. The plunger is of unitary construction made of a .plastic foam material and dimensioned so as to fit in the syr- 3 Claims, 3 Drawing Figures PATENTEDAPR 18 m2 3,656,480

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I FM 25 5 SYRINGE Most syringes are of two general types: glass syringes and plastic syringes. In glass syringes, the plunger is a hollow glass cylinder, one end of which is closed off and precisely ground to a carefully controlled diameter which forms a close fit in the barrel of the syringe. The clearance between the syringe plunger and barrel must be held to a very close tolerance. The fit between the barrel and the plunger cannot be too tight, or the plunger will bind in the barrel. The fit cannot be too loose, or the fluid will escape between the plunger and the barrel, thereby destroying the accuracy of a measured dose.

Another difficulty with conventional glass syringes is that the ground portion of the plunger often becomes wetted by the fluid being injected. When this occurs, a thin film of the fluid is formed on the interior of the syringe barrel between the barrel and the plunger, as the plunger is drawn from the barrel. If the plunger is reciprocated only once, and the syringe is then sterilized, the presence of a thin film does not cause a serious problem. However, the syringe plunger in many procedures is reciprocated more than once, without the syringe being sterilized, and in such cases, the thin film is exposed to contaminants when the plunger is pushed inwardly. When the plunger is drawn outwardly if the film is contaminated, it can contaminate any fluid contents in the syringe. Moreover, if the plunger of the syringe is inadvertently touched by the user the contents can become contaminated, since the contaminants can be transferred from the plunger to the thin film on the barrel, and into the fluid in the syringe. Such problems arise when two fluids are to be mixed by one fluid being drawn into the syringe, and then expelled into a reservoir of another fluid, and the mixture then drawn into the syringe. This can also occur when more than the capacity of the syringe is to be injected, and several reciprocations of the plunger are required.

Additionally, glass syringes are somewhat heavy, and relatively expensive, due to the careful grinding of the plunger required. Glass syringes are also breakable, and often are broken during sterilization of the syringe for reuse.

in order to overcome several of these problems, inexpensive plastic syringes have been provided. Such syringes due to their low cost can be disposed of after a single use, thus eliminating the need for sterilization. Furthermore, plastic syringes can be lightweight, and virtually unbreakable.

The plastic syringes are of several different types. The most commonly used plastic syringe is composed of a rigid and transparent plastic barrel, normally made by injection molding, which is fitted with a two-piece plunger. One piece of the plunger is a relatively rigid plastic stem, which is X-shaped or cross-shaped in cross section. The other piece is a resilient sealing member, such as a rubber piston, or an O-ring fitted on the pumping end of the stem. A relatively tight compression seal is formed between the barrel and the plunger, due to the resilience of the rubber sealing member. Since the seal is a resilient compression seal, there is considerable tolerance permissible in the size of the sealing member, as compared to the precision with which glass plungers are made. Moreover, the plastic material of the barrel and the rubber of the sealing member are often of a nature that they are not wetted by the particular fluid being injected. Thus, the possibility of contamination of the fluid contents of the syringe due to the formation of a thin film on the interior of the barrel is eliminated. It can therefore be appreciated that this type of plastic syringe has several distinctive advantages, as compared to a glass syringe. This type of plastic syringe, however, can only be used once, since it is not feasible to sterilize it for reuse. In the type of plastic syringe described above, it is necessary to disassemble the rubber piston or O-ring from the plunger stem, sterilize the barrel and both of the stem and sealing members, and reassemble the components under sterile conditions before the syringe can be reused. As can be appreciated, this is a timeconsuming and difficult process.

Other plastic syringes which can be sterilized have been provided. Such syringes are composed of only two pieces, a

barrel and a plunger both made of a plastic material. The plunger is made of a resilient plastic material and has a sealing portion near the distal end dimensioned so as to engage, and to an extent be compressed against the barrel, and form a seal thereagainst. Such a syringe is shown in US. Pat. No. 3,026,872 to Prater, Jr. Since the plunger is hollow and resilient, distortion can result if a particularly viscous fluid is being injected. Such distortion can cause the plunger to bind in the barrel.

Another plastic hypodermic syringe is shown in US Pat. No. 2,575,425 to Nelson. This patent discloses a syringe also composed of two plastic members, a plastic barrel and a plastic plunger. In this syringe the plunger is formed of a solid nylon rod, and has a flared end or skirt which forms a resilient flex-action seal against the barrel. One drawback of this syringe is that a solid plunger made of a plastic material, particularly nylon, results in a relatively heavy syringe, and also substantially increases the cost of the syringe due to the fact that a relatively large amount of plastic material must be used. This is especially true in the case of syringes of large capacity, for example, 50 cc.

In the one piece plastic plunger constructions described above, the effectiveness of the seal is dependent on the compressibility and resilience of the particular type of plastic material used. Although many plastics are compressible and are resilient, nevertheless the extent to which these properties can be used to effect a sliding-fit seal is limited by the fact that the plunger must be strong enough to resist deformation due to the force applied to the plunger in injecting a viscous liquid. Therefore a delicate balance between the resilience and compressibility of the plastic material and the strength required for the plunger must be maintained. The result is that in order to make a plunger that is both strong and forms a reliable seal, the plastic plunger still must be very carefully formed to rela tively close tolerances. Naturally, if the plunger is used often the plastic will tend to wear and the close tolerance, and con sequently the seal, will be lost. Furthermore, not all plastics which otherwise could be used for the plunger are compressible and resilient enough to form a good sea].

This invention provides a'syringe which is lightweight, and capable of being easily and repeatedly sterilized for reuse. The plunger is strong but is quite compressible and resilient and forms a good sliding-fit seal in the barrel. The syringe construction is simple and the syringe can be fabricated inexpensively and therefore can be discarded or sterilized and reused, as the user desires.

The syringe of the invention comprises, in combination, a syringe body, having an aperture at an end thereof for entry of fluid into, and exit of fluid from, the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid therefrom via the aperture, said plunger being made at least in part of a plastic foam material and being dimensioned and so fitted in the body so that the plastic foam material of the plunger forms a resilient compression seal against the body.

In the drawings:

FIG. 1 is a view in cross section of a syringe in accordance with the invention incorporating a plastic foam plunger FIG. 2 is an enlarged view of a portion included within the broken circle of FIG. 1 showing in detail a portion of the plunger, and

FIG. 3 is a view in cross section of another embodiment of a syringe in accordance with the invention.

As indicated above, the syringe plunger of the invention is made at least in part from a plastic foam which forms a resilient compression seal against the barrel. The plastic foam is particularly desirable since it can be formed into a very light but strong plunger which seals extremely well against the wall of the syringe barrel. This is due to the fact that the plastic foam is highly compressible and is extremely resilient, especially in thin sections, such as can be used to form the seal.

The compressibility and resilience of the plastic foam plunger is not a function merely of the resilience of the plastic material itself, but is also a result of the resilient nature of the thin-walled cellular structure of the plastic foam. The foam preferably is of the closed cell type, although it can also be of the open cell type. In either type, the combination of the gas within the cells which is compressible, and the thin walls of the cells of this structure make the plunger resilient, although the plastic material itself in a like thickness may be rigid. Thus, plastic materials which otherwise might be too rigid, and not sufficiently compressible to form a good seal against the barrel, can be made sufficiently resilient when in foam form to form a good seal. Moreover, foamed plastics due to their compressibility can be made to fit snuggly in the syringe body and can form a good seal therewith, over a wide range of thicknesses. Thus, the plunger diameter need not be held to a very close tolerance at the sealing surface.

Although closed cell foams are preferred open cell foams can also be used but they are less preferred. The open cell foams do not have gas trapped within each cell, but the open cells are nevertheless filled with air and the air acts as a resilient cushion or spring which aids in providing a good seal. If an open cell foam is used, it is important that there be no exposed or open through cells extending from one side of the plunger to the other, since such cells could cause leakage.

Foams of semi-rigid plastic material are preferred, since they provide good structural strength for the plunger, and yet are still resilient enough in cellular form to form a good seal. Somewhat flexible foam materials can also be used, provided they have sufficient structural strength to withstand, without severe deformation, the pressure applied in pumping fluid from the barrel of the syringe. Relatively flexible foams can often be used in larger size syringes since the rigidity of such foam materials increases as an exponential power of the thickness.

The syringe plunger preferably has a non porous and continuous surface layer throughout, to form a continuous smooth outside sealing surface abutting the syringe body, so that no through pores or open cells which could possibly cause leakage are exposed. This surface layer can be an integral skin formed on the plunger during the foaming and molding process used to make the plunger. The manner in which foamed plastics are made, and especially those foamed plastics having an integral skin, are well known to those of ordinary skill in the art and form no part of the present invention per se.

As a further possibility, the sealing layer can be coated onto the plunger after it is formed by well-known techniques.

It is also desirable to have a lubricating agent such as silicone, impregnated in, or coated onto, the surface layer to aid the plunger in sliding the syringe barrel and to aid in forming a tight seal.

The plastic material of the plunger is preferably one which is not wetted by the fluids being injected. Such plastics tend to prevent leakage or capillary action which could permit the fluid to form a film along the interface between the plunger and the barrel. Hydrophobic plastics are usually suitable, since many fluids that are administered via syringes are aqueous in nature. The resilient compression seal against the barrel provided by the foamed plastic plunger also aids in preventing the formation of a film, since it has a wiping action against the barrel surface. The plastic should also be inert to the chemicals with which it will come into contact and the foam should not contain any chemicals which possibly could leak out and cause irritation or more serious effects on the patient. Some preferred plastics, which may be polyolefins or vinyls, which form good foams suitable for use in making the plunger of the invention are polypropylene, polyethylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, polyurethane, cellulose acetate, phenolic resins such as phenolformaldehyde, ethylene vinyl acetate copolymer, ethylene ethylacrylate copolymer, silicone rubber, and ABS rubber. Other plastic materials and blends of plastic material can also be used providing their foamed form has the requisite properties specified above.

The plunger preferably is made entirely of foamed plastic material. However, if desired, it is possible to form the plunger all in one piece, but with only the sealing portion of the plunger of foamed plastic. One way in which this can be done is by forming the plastic into the desired plunger shape in a mold, and introducing the foaming agent only into the portion of the plastic which is to form the sealing portion of the plunger. Upon heating, the sealing portion will be foamed, but the remainder will not be foamed. In this manner, the resulting plunger although all in one piece is only foamed in the portion that seals against the barrel of the syringe.

The plunger can be elongated, and is generally cylindrical in shape. The plunger need not be cylindrical throughout its entire length. The stem portion of the plunger can take any desired cross sectional shape.

The sealing means is formed integrally with the plunger, as a portion thereof. It is preferred that the sealing means comprise a protruding portion at the distal end of the plunger, which is of greater diameter than the plunger body or stem. The sealing means preferably comprises one or more flanges, lips, rings, or a skirt or flare on the plunger end. The shape of the sealing means is not critical to the invention but should permit the plunger to slide with a minimum of resistance from one end to the other of the syringe. The sealing means shown in the drawings have been found to provide a particularly good relatively fluid-tight sliding seal. The sealing means is of a diameter which is greater than the inside diameter of the barrel, so that the sealing means engages the syringe barrel, and is compressed to form a sliding resilient compression seal against the inside surface of the barrel which preferably wipes the barrel clean of fluid adhering thereto as it passes. The portion of the sealing means which contacts and engages the barrel can be relatively thin, since thin sections of the plunger material are quite resilient and compressible.

The end of the plunger which is to be held by the hand of the user can be formed with a flattened or flared portion, or into a ring shape so that it can be conveniently gripped.

The syringe body has a barrel, and an apertured tip at the end of the barrel. Normally, the syringe also has a flare, flange or tabs at the opposite end of the barrel so as to facilitate gripping of the syringe by the user. The apertured tip normally is formed into a Luer type fitting for connection to Luer needles and connectors.

Any of the conventional materials normally used for syringe barrels can be used. The barrel is preferably transparent but it can be merely translucent, so that the plunger can be aligned with the graduated markings on the side of the barrel.

The syringe shown in FIG. 1 comprises a body I having a cylindrical barrel 2, a flanged end 3 at one end of the barrel, and an apertured Luer tip 4 at the opposite end thereof for connection to a Luer needle. A foamed plastic one piece plunger 5 is positioned in the barrel of the syringe. The distal end of the plunger is formed into a series of protruding sealing ribs 16 which are of slightly greater diameter than the barrel. These rings are compressed in the barrel and form a relatively tight but slidable resilient compression seal against the barrel. At the opposite end of the plunger a flare 10 is formed. The foamed plastic plunger 5 includes a large number of closed gas-containing cells 12. The cells 12 can best be seen by reference to FIG. 2. Additionally, an integral skin 15 of the plastic material is formed at the surface of the plunger. This skin forms a good sealing surface for the ribs 16.

Another embodiment of the syringe of the invention is shown in FIG. 3. In this embodiment the plunger 20 is made of high density plastic foam and is mounted in a conventional glass syringe body 19. This plunger differs from that described above in that the sealing means is a resilient skirt or flare 22 formed on the end of the plunger. The flare 22 is of slightly greater diameter than the barrel and is compressed and deflected into sealing engagement with the barrel. The end of the plunger is formed with a concave portion 23. The configuration of the flare 22 and the concave portion 23 is particularly desirable since the resilient sealing of the flare 22 against the barrel is assisted by the force exerted on the flare by the fluid trapped within the concave portion 23 of the plunger as the fluid is expelled from the barrel by the plunger. The opposite end of the plunger is formed into a ring 24 which is adapted to accommodate the thumb of the user.

Both the syringes of FIGS. 1 and 3 can be subjected to sterilizing temperatures in excess of 212 F. without deterioration of the plunger or barrel since the particular plastics that may be employed have a high melting point. The syringes are lightweight and inexpensive to make, and can be discarded after a single use, if desired. However, since the syringes shown in FIGS. 1 and 3 can be sterilized, and since the plungers are interchangeable between syringe bodies of the same size due to the resilience of the plastic foam plunger, it is possible to bulk sterilize syringes of the invention and automatically sort the syringe plungers and barrels according to size, for reassembly and reuse. This is not possible with glass syringes since the plungers and barrels are not interchangeable and the sorting of large groups of syringes to ensure that the correct plunger is reassembled into its mating barrel would be a very time consuming process.

As noted above, however, this can be done with the syringes of this invention since for a given syringe size the plungers are interchangeable among the syringe barrels of that size. Sorting of bulk sterilized syringes can be done by color coding the syringe plungers and barrels. This can be done by providing a band of the same color both on the barrel and the plunger of the syringes of a given size. It is also possible to tint the entire barrel a given color and also solidly color the plunger. Sorting of syringe plungers and barrels can then be carried out according to size by automatic sorting machines which are well known in the sorting art. One suitable machine is manufactured by the Electric Sorting Machine Division of Mandrel Industries, Inc. of Houston, Texas. As a further possibility, the syringe barrels and plungers can be sorted magnetically in the same manner. This can be done by impregnating the barrel and the plunger with a ferromagnetic material which can be arranged in a form so as to serve as a coded identification of the syringe barrels and plungers according to size. Magnetic sorting machines are also known to those skilled in the art. The syringe shown in FIG. 1 may have a color code in the form of a circumferential color band 25 on the barrel and a matching color band 26 on the plunger for automatic sorting of the plunger and barrel. The syringe shown in FIG. 3 may have a color code in the fon'n of a tinting of the barrel and a solid matching color of the plunger.

Having regard to the foregoing disclosure the following is claimed as the inventive and patentable embodiments thereof:

1. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being of a closed cell foamed plastic material and being dimensioned and so fitted in the body so that the foamed plastic material of the plunger forms a relatively fluid tight resilient compression seal against the body.

2. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being made of polyethylene foam and being dimensioned and so fitted in the body so that the plunger forms a relatively fluid tight resilient compression seal against the body.

3. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being made of polyurethane foam and being dimensioned and so fitted in the body so that the plunger forms a relatively fluid tight resilient compression seal against the body. 

1. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being of a closed cell foamed plastic material and being dimensioned and so fitted in the body so that the foamed plastic material of the plunger forms a relatively fluid tight resilient compression seal against the body.
 2. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being made of polyethylene foam and being dimensioned and so fitted in the body so that the plunger forms a relatively fluid tight resilient compression seal against the body.
 3. A syringe comprising, in combination, a syringe body having an aperture at an end thereof for entry of fluid into and exit of fluid from the body; a pumping plunger reciprocably movable in the body in a sliding fit in a manner to draw fluid into and expel fluid from the body via the aperture; said plunger being made of polyurethane foam and being dimensioned and so fitted in the body so that the plunger forms a relatively fluid tight resilient compression seal against the body. 